Bushing insulator improvements for a dead tank vacuum switch

ABSTRACT

A vacuum switch is of the type having a metallic or other material electrically dead enclosure through which one or more conductive terminal leads extend. Interposed between each terminal lead and enclosure is a respective, preferably ceramic, insulator bushing. Annular, semi-flexible metal sealing means are at one limit embedded in (or could be sealed to) the insulator ceramic and at other limits metal-to-metal secured to an enclosure tank part and metal-to-metal secured to terminal lead. Metal support means for metal condensing shields may extend from embedment in the ceramic material and be metal-to-metal bonded similarly.

United States Patent Luehring [451 Dec. 5, 1972 [s41 BUSHING INSULATOR IMPROVEMENTS FOR A DEAD TANK VACUUM SWITCH v [72] Inventor: Elmer L. Luehring, Cleveland Heights, Ohio [73] Assignee: Joslyn Mtg. and Supply Company,

Chicago, 111.,

[22] Filed: April 29, 1971 v [21] Appl. No.: 138,563

[52] us. C1. ..200/144'1:

[51] Int. Cl. ..ll0lh 33/66 [58] Field or Search ..200/144 B [56] References Cited UNITED STATES PATENTS 3,590,185 6/1971 Pflanz ..200/144 B FOREIGN PATENTS OR APPLICATIONS 1,125,705 8/1968 Great Britain ..200/144 B Prim'ary Examiner-Robert S. Macon Attorney--Richard MacCutcheon [57] ABSTRACT I A vacuum switch is of the type having a metallic or other material electrically dead enclosure through which one or more conductive terminal leads extend. lnterposed between each terminal lead and enclosure is a respective, preferably ceramic, insulator bushing. Annular, semi-flexible metal sealing means are at one limit embedded in (or could be sealed to) the insulator ceramic and at-other limits metal-to-metal secured to an enclosure tank part and metal-to-metal secured to terminal lead. Metal support means for metal condensing shields may extend from embedment-in the ceramic material and be metal-to-metal bonded similarly.

1 Claim, 1 Drawing Figure PATENTED 5 I97? INVEN TOR. ELMER L. LUEHRING ATTORNEY BUSHING INSULA'IOR IMPROVEMENTS FOR A DEAD TANK VACUUM SWITCH CROSS REFERENCE TO RELATED APPLICATION In my co-pending application (H 61) (Ser. No. 138,562, now US Pat. No. 3,670,123, issued June 13, 1972, and assigned to the assignee of the present-invention,'constructions and uses are described for a pluralway to common point switch of av type which is protected against ambient (e.g., a highvacuum switch) and which has a dead (e.g., electrical ground) outer tank. As shown in that application, operating rods extend out the bottom of the tank while plural topthreaded conductive studs for the stationary contacts stop short of coming out of the tanks other end. Instead, each is substantially isolated within insulation both shown and unshown, it being assumed that the threaded end of each stud is for ultimate mating with a removable. cable or with a. removable bushing associated witha conductor cable and having, perhaps,

outerishield metal, intermediate plastic insulation, and

an innerconductive metal material. l

: BRIEFDESCRIPTION OF THE DRAWINGS An object of the present invention is to provide simple means for overcoming the above mentioned difficulties.

Other objects and advantages will become apparent from consideration of the following description taken in connection with the accompanying drawing, in-

which: P

- The single drawing FIGURE is a sectional elevation of a portion of a dead+tank switch having improvements according to the present invention.

DESCRIPTION OF PREFERRED EMBODIMENT The drawing shows a movable switch contact 11 designed for mating with a stationary contact 12. No conductive lead or plate is shown for the movable contact, as there are various ways of getting out of the tank, even in accordance with the present invention, as may be more apparent as the description proceeds.

The movable contact 11 is controlled through an insulation section 24 by a pull rod 2l which extends through a bellows 23 to the outside of what will be described as a vacuum enclosure or tank, e.g., having a top, a cylinder wall, and a bottom, as at 5ST, 55C and 55B.

Conductively related to stationary contact 12 is a terminal connector or stud 51 at the top of which is an external terminal portion 1. A condensing shield 27 is preferably approximately concentric with the contacts II and I2 while insulated electrically from the contacts, and from conductive parts associated with the contacts, and from the enclosure.

An insulator bushing body supports and insulates all of stud 51, contact 12 and shield 27 while provided with annular metal seal flanges 61 and 62, each extending from intimate (e.g., embedded during bushing molding) association with bushing 60 to intimate association with metal.

Bushing body 60 may be substantially one-piece molded from molten glass with seal and/or support flanges embedded. Metal seal 61 may be fusion welded to the wall of an aperture in the tank and metal seal 62 fusion welded either to stud'51 or to a flange 63 previously associated with the stud. An annular flange 64 may be embedded in the glass (or other)material of bushing 60, and then condensing shield 27 may derive its support by being spot welded to the flange 6 4.

As shown, bushing 60 has two inner diameters. The smaller i.d. surface 65 of bushing 60 is preferably coated with a material such as a conductive glaze or paint 66 which can electrically connectwith seal 62 and which. also electrically shields (or excludes) any airspace between stud 51 and bushing 60.

V While it forms no part of the present invention, there maybe a movable contact support member 26 and a lower cup-like shield means 52, as in the co pending application, and liketerminals (not shown in instant case) may be used elsewhere to again pass through the tank enclosure. A

SUMMARY OF ADVANTAGES There is thus provided apparatus capable of meeting the object set forth while providing many additional advantages as well. The combination of annular metal seals, assumed to have design parameters rendering them sufficiently flexible, and the bushing not only (a) overcome any problem of different thermal expansions and (b) obviate need of any removable part within an insulator material shield or conductor bushing (thus ex-' cluding chance of entry of air, water, or other contaminants) but (c) combine in one. predominantly insulator part 1 an insulating support for a condensing .(metal) shield, 2 an insulating bushing for a terminal connector, 3 a vacuum seal for the switch,.4 an insulating support for necessary switch parts (e.g., stationary contact plus condensing shield), 5 a reduction in number of parts, 6 a design providing easy moldability of a preferential material, such as glass, forthe bushing, 7 more flexibility in selecting means employed for connection of cable (not shown), and 8 a great reduction in size and weight and cost of bushing (e.g., with respect to creepage path) and thus of vacuum chamber as contrasted with size for comparable rating required by the design described in the co-pending application or by any prior art design for a dead tank non-air-break switch.

Heretofore most discrete insulator bodies or bushings for high voltage (e.g., above 1 KV) have been made of porcelain (sintered Kaolin, feldspar and quartz).

But I have found that glass has excellent properties for high voltage insulator bushings. lts mechanical and dielectric properties are adequate, and moreover, as contrasted with procelain,

1. Greater accuracy can be achieved with glass, because it can be molded and has no directional shrinkage variations, which, for high voltage uses as herein described, is highly advantageous,

2. Greater design flexibility as regards sealing and support capabilities are achieved .with glass because of the possibility of metal embedment therein (the melting point of glass being less than that of most metals while the firing temperature of 5 porcelain is higher than the melting point of most metals, so that metal connections to porcelain can only be made by the plural steps of metallizing and then brazing or soldering after ceramic vitrification).

For either of the co-pending application or instant case, there is of course a creepage path along insulation from high voltage conductor (or its support flange) to dead-tank" (or to metal seal associated therewith). But in the present case, the creepage path, e.g., from 51, 66, 62 around inside, across bottom, and up the outside of bushing 60 to 61 and thus to tank is not only long but it can be and is interrupted by a support flange (64) for a part (27) which is electrically isolated.

Equivalents have to be considered. A round bushing with around inner opening might be less expensive than a square one onlyfor he who need not consider an outstanding patent. Thus it is desired that the words diameter and dimension be considered as interchangeable insofar as construing the claims hereinafter is concerned. For while I have illustrated and described a particular embodiment, various modifications may obviously be made without departing from the true spirit and scope of the invention which I intend to have defined only by the appended claims taken with all reasonable equivalents.

Thus, having a bushing of glass can be only one species or sub-combination of the invention for it is possible to secure metal to glass by means other than embedment. For example, heating and a shrinkage fit can be used though there might still be dimensional troubles elsewhere if porcelain is used for the body of the insulator bushing.

Further, the present invention does not seem limited just to switches. It could have applicability to transformers, potheads, generators, and other devices lclaim:

In a high voltage device, the combination of a metallic housing which is electrically grounded and which serves as a major portion of an enclosure which seals against ambient air,

a pair of matable contacts within the enclosure, one of said contacts being relatively stationary and the other being relatively movable for selective engagement with the stationary contact,

a terminal connector stud associated with the stationary contact,

an insulator bushing which surrounds said connector stud and which extends from a locale considerably within the enclosure to locale considerably outside the enclosure,

first semi-flexible means, said first means surrounding and supporting said bushing insulator from said housing while hermetically sealing the combination of housing and bushing,

second semi-flexible means, said second means surrounding and supporting said connector stud from the bushing while hermetically sealing the combination of bushing and connector stud by its intimate contact with both of bushing and stud at a locale which is well within the enclosure, an electrically floating shield which 15 arranged about the contact pair,

a third semi-flexible means, said third means surrounding and supporting said shield from said bushing while the bushing surrounds the predominance of the third semi-flexible means and thus surrounds the shield,

said insulator bushing having first and second inner diameters the first of which relatively closely surrounds the connector stud and has a conductive coating which electrically connects with the second semi-flexible means, while the second inner diameter of the insulator bushing surrounds at least a portion of the shield, provides attachment for the third semi-flexible means, and elongates creepage paths internally of the enclosure and extending from housing to shield, from shield to stud, and thus from housing to stud except for the conductivity, if any, of the sealing means, whereby to reduce size and weight and cost of the overall device required for any particular electrical rating. I 

